Both the European Food Safety Authority (EFSA)^[3] and the United States Food and Drug Administration (FDA) have evaluated TBHQ and determined that it is safe to consume at the concentration allowed in foods.^[4] The FDA sets an upper limit of 0.02% of the oil or fat content in foods.^[5]

At very high doses, it has some negative health effects on lab animals, such as producing precursors to stomach tumors and damage to DNA.

A number of studies have shown that prolonged exposure to very high doses of TBHQ may be carcinogenic,^[7] especially for stomach tumors.^[8] Other studies, however, have shown opposite effects including inhibition against HCA-induced carcinogenesis (by depression of metabolic activation) for TBHQ and other phenolic antioxidants (TBHQ was one of several, and not the most potent).^[9] The EFSA considers TBHQ to be noncarcinogenic.^[4] A 1986 review of scientific literature concerning the toxicity of TBHQ determined that a wide margin of safety exists between the levels of intake by humans and the doses that produce adverse effects in animal studies.^[10] Michigan State University scientists are studying a possible link between TBHQ and food allergies.

https://en.wikipedia.org/wiki/Tert-Butylhydroquinone